Methods of removing sulfur from the exhaust gases of fired fuels containing sulfur and of simultaneously exploiting the sulfur for the preparation of sulfuric acid

ABSTRACT

AMMONIUM NITRATE AND AT LEAST ONE OF THE COMPOUNDS POTASSIUM NITRATE AND SODIUM NITRATE ARE INTRODUCED INTO THE EXHAUST GASES FROM A FURANCE FIRED WITH FUELS CONTAINING SULFUR, AND THE EXHAUST GASES ARE MIXED WITH STEAM IN A REACTION CHAMBER WHEREUPON THE EXHACUST GASES ARE COOLED AND THE FORMING SULFURIC ACID SOLUTION IS COLLECTED.

United "States Patent 3,786,136 METHODS OF REMOVING SULFUR FROM THE EXHAUST GASES OF FIRED FUELS CONTAIN- ING SULFUR AND OF SIMULTANEOUSLY EX- PLOITING THE SULFUR FOR THE PREPARA- TION OF SULFURIC ACID Tord Valter Yngve Axeborg, 360 75, Alstermo, Sweden No Drawing. Filed July 15, 1971, Ser. No. 165,783

Int. Cl. C01b 17/72 U.S. Cl. 423-522 8 Claims ABSTRACT OF THE DISCLOSURE Ammonium nitrate and at least one of the compounds potassium nitrate and sodium nitrate are introduced into the exhaust gases from a furnace fired with fuels containing sulfur, and the exhaust gases are mixed with steam in a reaction chamber whereupon the exhaust gases are cooled and the forming sulfuric acid solution is collected. a

This invention relates to a method of removing sulfur from the exhaust gases of fired fuels containing sulfur and of simultaneously exploiting the sulfur for the preparation of sulfuric acid.

In large central-heating stations such as heating plants, power plants, large apartment house and industrial heating stations which consume large quantities of fuel and in which it is therefore imperative that the fuel is inexpensive, thick oil of high sulfur content is used to an ever increasing extent. At the same time the discharge from the chimneys of sulfur dixoide and sulfur carbon black forming at the combustion has become an ever more difiicult problem because of the environmental damage and the risk to human health which accompany their discharge into ambient air. To purify the thick oil before use or to substitute for it an oil of higher quality would entail high costs and besides would not provide a complete solution of the problem since some sulfur dioxide and sulfur carbon black would still escape through the chimneys, polluting the ambient air.

This invention has for its object to provide a solution of the problem outline above, by which solution the sulfur is practically completely removed from the exhaust gases when fuels containing sulfur are fired and also when thick oil of high sulfur content is fired, simultaneously as the sulfur is exploited for the preparation of sulfuric acid of which large quantities are consumed by the industry. In applying the invention it is therefore even possible to supply additional sulfur in connection with the combustion of the fuel containing sulfur with a view to recovering a larger amount of the valuable sulfuric acid.

The method suggested by the invention comprises the steps of introducing into the firing flame ammonium nitrate and at least one of the compounds potassium nitrate and sodium nitrate, mixing the exhaust gases from the furnace, before they are deflected into the chimney, in a reaction chamber with steam, cooling the thus obtained mixture of exhaust gases and reaction products, and collecting the condensing sulfuric acid solution. The nitrates can be either added in pulverulent form or injected in the form of an aqueous solution.

The addition of the nitrates provides a large oxygen excess at the combustion and therefore an almost 100% combustion is attained, for which reason the formation of carbon black, such as sulfurcarbon black and flue carbon black, as well as the formation of coatings is prevented.

The addition of the nitrates can be performed directly to the firing flame, or the nitrates may be added to the fuel and introduced into the firing flame with the fuel.

In a particular chamber constructed by or internally lined with acid-resistant material, the exhaust gases are mixed with steam which is blown into the chamber. This chamber may be a reaction tower fiilled with acid-resistant material having a large free surface, as is often the case nowadays at the preparation of sulfuric acid according to the lead chamber process.

Because of the presence of large amounts of nitrogen, deriving particularly from the ammonium nitrate and the air supplied for the combustion, and the presence of steam, the sulfur dioxide will be converted by catalysis with the aid of nitrogen oxides into sulfur trioxide and sulfuric acid, the reaction occurring substantially in the same way as in the well-known lead chamber process for sulfuric acid production, with the formation of nitrosyl sulfuric acid as a non-iso1ated intermediate.

Leaving the reaction chamber, the reaction mixture containing the remaining exhaust gases and the sulfuric acid formed, is passed through a cooling device in which the sulfuric acid condenses. The condensing sulfuric acid is allowed to flow and collect in a chamber or container to which is led also the sulfuric acid that accompanies the exhaust gases and condenses on the walls of the chimney.

The formation of sulfuric acid is an exothermal reaction and the reaction heat slightly increases the exhaust gas temperature, which contributes to eliminating deposition of insulating coatings on the walls of the exhaust gas channels. Of course, all wall surfaces coming into contact with the sulfuric acid must be of acid-resistant material.

Owing to the sulfur content of the fuel and the amount of steam supplied it is possible to obtain sulfuric acid of various strength, from about sulfuric acid having a specific weight of 1.83 to Glover acid, chamber acid or battery acid.

Should the reaction rate be too low in some cases so that a complete conversion of the sulfur dioxide formed into sulfur trioxide would not occur with the system de scribed in the foregoing, a complete reaction can be obtained with the aid of contact catalysts, particularly vanadium or platinum catalysts.

By the addition to the fuel or to the firing flame of the above mentioned nitrates practically all carbon black and other solid particles will be eliminated from the exhaust gases and at the same time depositions are avoided in the furnace and the exhaust gas channels. To remove also the small amounts of dust particles or flue carbon black which may still occur in the exhaust gases for obtaining a purer acid a dust separator, preferably an electro-filter, may be inserted at some point in the exhaust gas channels before the reaction chamber where the exhaust gases are mixed with the steam.

Apart from the above mentioned nitrates a small amount of pulverulent sulfur may be added to the fuel or to the firing flame as a combustion accelerator Which contributes to ensuring a complete combustion of the fuel. In this connection the sulfur addition may be increased over the amount required for the above purposes, if it is desired to increase the production of sulfuric acid.

It is not necessary to operate at elevated pressure to convert all sulfur into sulfuric acid, but work at atmospheric pressure is suflicient.

The addition made to the fuel or to the firing flame contains a major proportion of potassium nitrate and/or sodium nitrate and a minor proportion of ammonium nitrate, preferably in a weight ratio within the ranges of about 4:1 to 8:1. Use is preferably made of potassium nitrate in an amount greater than that of the sodium nitrate. It is, however, advantageous to add part of the requisite nitrate in the form of sodium nitrate because of the rust protective action it exerts. The amounts of the various constituents of the addition preferably are comprised within the following limits:

Ammonium nitrate: 10-20% by weight, preferably 12-18% by weight Potassium nitrate: 40-85% by weight, preferably An example of the composition of a suitable addition is 17% by weight of ammonium nitrate and 83% by weight of potassium nitrate. Another example is 12% by Weight of ammonium nitrate, 44% by weight of potassium nitrate and 44% by weight of sodium nitrate. Still another example is 17% by weight of ammonium nitrate, 73% by weight of potassium nitrate and 10% by weight of sodium nitrate. Possibly, a small amount of sulfur such as 112% calculated on the total weight of ammonium, potassium and sodium nitrate, may be added thereto.

The amount of the above addition to be made to the fuel or to the firing flame should be adapted to the type and quality of the fuel. It is suitably added through a dosing apparatus connected to a fuel gauge so that the amount of addition is regulated in relation to the fuel supply.

The invention is primarily intended for application to the firing of oils containing sulfur, but it can also be applied to the firing of solid fuels containing sulfur.

What I claim and desire to secure by Letters Patent is:

1. A method for removing sulfur oxides from exhaust gases obtained by burning fuels containing sulfur comprising burning said fuels in the presence of air and ammonium nitrate and at least one compound selected from the group consisting of potassium nitrate and sodium nitrate, the amount of ammonium nitrate by weight being about A; to about A of the amount of the at least one other nitrate, the total amount of nitrates with respect to the fuel being burned being determined by the amount of sulfur therein, passing the gaseous combustion products into an acid resistant reaction chamber, introducing steam into the reaction chamber to convert sulfur trioxide formed during combustion of the fuel into sulfuric acid, cooling the products formed in the reaction chamber to condense sulfuric acid, recovering the sulfuric acid and venting the substantially sulfur free gaseous combustion products to the atmosphere.

2. A method as claimed in claim 1 and further comprising the step of removing dust particles from the combustion products prior to the introduction thereof into the reaction chamber.

3. A method as claimed in claim 1 and further comprising burning the sulfur containing fuels in the presence of a catalyst for converting sulfur dioxide into sulfur trioxide.

4. A method as claimed in claim 1 wherein the nitrates are added to the fuel before burning.

5. A method as claimed in claim 1 wherein the nitrates are supplied to the fuel at the point of combustion.

6. A method as claimed in claim 5 wherein the nitrates are supplied in pulverulent form to the fuel.

7. A method as claimed in claim 5 wherein the nitrates are supplied to the fuel in aqueous solution.

8. A method as claimed in claim 1 wherein the amount of steam introduced into the reaction chamber is determined in accordance with the desired strength of the sulfuric acid produced.

7 References Cited UNITED STATES PATENTS 2,111,276 3/1938 Castner et al. 23-158 2,510,684 6/1950 Cathala 23--174 1,833,418 11/1931 Fairlie 23168 FOREIGN PATENTS 147,091 10/1921 Great Britain 23158 13,171 8/ 1895 Great Britain 23-167 EDWARD J. MEROS, Primary Examiner G. A. HELLER, Assistant Examiner US. Cl. X.R. 423532, 539, 242 

